The invention relates to a process for the manufacture of semiconductor wafers with a rear side having a gettering action in subsequent high-temperature processes. More particularly, it relates to such a process wherein dislocation networks are formed in the surface region of the rear side of the wafer by the action of light radiation.
In the manufacture of electronic components from semiconductor wafers, the point defects and impurities in the wafers are often the cause of undesirable phenomena, such as, for example, increased leakage currents at barrier layers and capacitors of integrated circuits.
Such point defects, point defect clusters and impurities can, however, be removed or "gettered" through the rear side of the wafer by various processes so that the front side of the wafer is free of defects being produced in the rear side of the wafer by means of certain treatments. During the high-temperature processes carried out in the course of the manufacture of semiconductor components, such as, e.g., oxidation at, usually, from 800.degree. to 1250.degree. C., these defects then exhibit their gettering action and draw or suck off the point defects, point defect clusters and impurities present in the wafer through the rear side of the wafer. One possible method of manufacturing such a wafer having a rear side with a gettering action comprises, for example, subjecting the rear side of the wafer to mechanical stress, for example by immersing it in a fluid bath of moving abrasive grains (cf. DE-OS 29 27 220), or by directed scratching (cf. U.S. Pat. No. 3,905,162). In those processes, however, there is always the risk of impurities because of the contact of the wafers with mechanical abrasives.
This risk can be avoided by treating the rear face of the wafers by laser radiation. It is known, for example according to U.S. Pat. No. 4,131,487, to vaporize semiconductor material in individual surface areas by laser treatment and thus to produce areas that have a gettering action in subsequent oxidation processes. However, this process requires a considerable expenditure of energy, involves loss of material and, in addition, as a result of the formation of vaporization pits or craters, impairs the surface qua1ity of the semiconductor material so that, e.g., problems may arise when sucking down the wafers using vacuum chucks. Also, the process according to DE-OS 28 29 983, in which a layer on the rear side of the wafer is vaporized by a first laser pulse and then the dislocation network necessary for the gettering is produced by a second laser pulse, is similarly already expensive as far as energy is concerned, because of the vaporization step.
By contrast, processes according to which layers in the surface region of the semiconductor wafers are not vaporized but only melted require lower intensities of radiation energy. But in these processes too, as described, e.g., in J. Electrochem. Soc. 128. pages 1975-80 (1981), in Extended Abstract No. 485 Los Angeles Meeting Electrochemical Society, 14.-19.10.1979, and in U.S. Pat. No. 4,257,827, the energy requirement is still considerable and does not permit a broad economical use of this laser treatment, referred to as "laser damage" in technical language, for the rear side gettering of semiconductor wafers.